Giardiasis Overview

Giardiasis is an infection of the small bowel by a single-celled organism called Giardia lamblia. People become infected with the Giardia parasite after swallowing Giardia cysts often found in water contaminated by raw sewage or animal waste.

In the US, Giardiasis is the most common intestinal parasitic disease.

Travelers to foreign countries may develop diarrhea often caused by Giardia.

Giardiasis Causes

Giardia cysts are transmitted to humans in various ways.

Contaminated water supplies: Giardia is one of the most common causes of water-borne diarrhea outbreaks. Sources of contaminated water include public facilities that improperly filter and treat water, water in developing countries, or rivers and lakes used by hikers. Overseas travelers and hikers are at a high risk for infection.

Contaminated food: Food that may have been washed in contaminated water, exposed to manure, or prepared by an infected person can transmit the disease.

Person-to-person contact: Infection may be caused by poor hygiene and most commonly occurs in daycare centers, nursing homes, and during oral-anal sexual contact. Family members, daycare workers, and others in contact with infected stool may then themselves become infected.

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Giardia lamblia was originally identified by von Leeuwenhoek in the 1600s and was first recognized in human stool byVilem Dusan Lambl (1824-1895) in 1859and by Alfred Giard (1846-1908) after whom it is named.